The term “decorative panel” in the sense of the invention means wall, ceiling or floor panels comprising a decor applied onto a carrier plate. Decorative panels are used in a variety of ways both in the field of interior design of rooms and for decorative cladding of buildings, for example in exhibition stand construction. One of the most common uses of decorative panels is their use as a floor covering. Herein, the decorative panels often comprise a decor intended to replicate a natural material.
Examples of such replicated natural materials are wood species such as maple, oak, birch, cherry, ash, walnut, chestnut, wenge or even exotic woods such as Panga Panga, mahogany, bamboo and bubinga. In addition, often natural materials such as stone surfaces or ceramic surfaces are replicated.
Heretofore, such decorative panels are often produced as laminates, in which a decorative paper pre-printed with a desired decor is applied onto a carrier plate and in turn a so-called overlay is applied onto the decorative paper. In order to avoid a deformation of the decorative panels, the so-called cupping, by shrinkage effects of the applied decorative paper, subsequently a backing paper is applied onto the side of the carrier plate opposite to the decorative paper and the layered structure obtained is firmly bonded together using appropriate pressure and/or heat-activated adhesives. Herein, the forces acting onto the carrier plate by the backing layer should counteract the tensile forces caused by the cupping.
Herein, the application of the backing layer requires a further process step and, thus, increased production costs.
In dependence of the desired field of application of these decorative panels they can be made of different materials. Herein, in particular, the material of the carrier can be selected depending on the field of application. Thus, the carrier may for example consist of a wood-based material, provided the decorative panels are not exposed to excessive moisture or weather conditions. However, if the panel is intended to be used, for example, in wet rooms or outdoors, the carrier may for example consist of a plastic material.
Wood-based materials in the sense of the invention in addition to solid wood materials are materials such as cross-laminated timber, glue-laminated timber, blockboard, veneered plywood, laminated veneer lumber, parallel strand lumber and bending plywood. In addition, wood-based materials in the sense of the invention are also chipboards such as pressboards, extruded boards, oriented structural boards (OSB) and laminated strand lumber as well as wood fiber materials such as wood fiber insulation boards (HFD), medium hard and hard fiberboards (MB, HFH) and in particular medium density fiberboards (MDF) and high density fiberboards (HDF). Even modern wood-based materials such as wood polymer materials (wood plastic composite, WPC), sandwich boards made of a lightweight core material such as foam, rigid foam or honeycomb paper and a layer of wood applied thereto, and minerally hardened, for example with cement, chipboards are wood-based materials in the sense of the invention. Moreover, cork represents a wood-based material in the sense of the invention.
Plastic materials which can be used for producing corresponding panels are, for example, thermoplastic plastic materials such as polyvinyl chloride, polyolefines (such as polyethylene (PE), polypropylene (PP)), polyamides (PA), polyurethanes (PU), polystyrene (PS), acrylonitril butadiene styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyether ether ketone (PEEK) or mixtures or co-polymerizates thereof. The plastic materials can include common fillers, such as calcium carbonate (chalk), aluminum oxide, silicagel, quartz powder, wood flour, gypsum. In addition they can be coloured in a known way.
The term “direct printing” in the sense of the invention means the application of a decor directly onto the carrier of a panel or onto an unprinted fiber material layer applied to the carrier. In contrast to the conventional methods in which a decorative layer previously printed with a desired decor is applied onto the carrier, in direct printing the decor is printed directly in the course of the surface coating or the panel manufacturing process. Here, different printing techniques such as flexographic printing, offset printing or screen printing may be used. In particular digital printing techniques such as inkjet processes or laser printing can be used.
In the sense of the invention the term fiber materials means materials such as paper and non-woven fabrics on the basis of plant, animal, mineral or even synthetic fibers as well as cardboards. Examples are fiber materials on the basis of plant fibers and, in addition to papers and non-woven fabrics made of cellulose fibers, boards made of biomass such as straw, maize straw, bamboo, leaves, algae extracts, hemp, cotton or oil palm fibers. Examples of animal fiber materials are keratin-based materials such as wool or horsehair. Examples of mineral fiber materials are mineral wool or glass wool.
For protecting the applied decorative layer normally wearing or top layers are applied on top of the decorative layer. A wearing and/or top layer in the sense of the invention is a layer applied as an outer border which in particular protects the decorative layer from wear or damage caused by dirt, moisture and mechanical impacts such as abrasion.
It is often intended that in such a wearing or top layer a surface structure matching with the decor is introduced. A surface structure matching with the decor means that the surface of the decorative panel has a haptically perceivable structure which with respect to its shape and pattern corresponds to the applied decor in order to achieve a reproduction of a natural material as close to the original as possible even with respect to the haptic.
A problem which may occur during direct printing of decorative panels is that the surface of the decorative panel to be printed is no optimal printing substrate onto which a corresponding decor can be applied. Here, the problem is that a paper or non-woven fabric layer applied as a printing substrate onto a carrier plate of a decorative panel is penetrated by the resin used for the application such that the resin applied for fixing penetrates through on the side of the paper or non-woven fabric intended to be printed and can cause adhesion problems of the printing ink there. To overcome this problem, the paper or non-woven fabric may be provided with a barrier layer that prevents the penetration of the resin through the paper or non-woven fabric. However, such a barrier layer often brings about that the ink applied in the printing process does not or not sufficiently settle into the paper or non-woven fabric, but remains on the surface, which adversely affects the quality of the print. Furthermore, it can be provided that the paper or non-woven fabric is provided with an ink receiving layer on the side to be printed prior to the application onto the carrier plate, and then the ink receiving layer is printed. The decorative paper thus prepared is then applied onto the carrier plate. However, during the subsequent application of a top or wearing layer adhesion problems can be caused, so that the final composite laminate has no sufficient stability and, for example, splitting of the laminate in the decorative paper layer is caused.